CN110261722B - Single-phase grounding judgment and phase judgment method of neutral point ungrounded system - Google Patents

Single-phase grounding judgment and phase judgment method of neutral point ungrounded system Download PDF

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CN110261722B
CN110261722B CN201910719647.2A CN201910719647A CN110261722B CN 110261722 B CN110261722 B CN 110261722B CN 201910719647 A CN201910719647 A CN 201910719647A CN 110261722 B CN110261722 B CN 110261722B
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voltage
value
characteristic voltage
phase
characteristic
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CN110261722A (en
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刘红文
王科
赵现平
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Electric Power Research Institute of Yunnan Power Grid Co Ltd
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01RMEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/08Locating faults in cables, transmission lines, or networks
    • G01R31/081Locating faults in cables, transmission lines, or networks according to type of conductors
    • G01R31/086Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution networks, i.e. with interconnected conductors
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01RMEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/08Locating faults in cables, transmission lines, or networks
    • G01R31/088Aspects of digital computing

Abstract

The application discloses a single-phase grounding judgment and phase judgment method of a neutral point ungrounded system, which comprises the steps of obtaining first, second and third detection voltages output by an external power supply; obtaining a first characteristic voltage reference value, a second characteristic voltage reference value and a third characteristic voltage reference value; obtaining current values of the first characteristic voltage, the second characteristic voltage and the third characteristic voltage; calculating and obtaining the phase difference between the current value of the first characteristic voltage and the reference value of the first characteristic voltage, the phase difference between the current value of the second characteristic voltage and the reference value of the second characteristic voltage, and the phase difference between the current value of the third characteristic voltage and the reference value of the third characteristic voltage; judging whether the number of the three phase difference absolute values exceeding a preset phase difference threshold value is less than or equal to 1; if so, taking the current value of each characteristic voltage as the reference value of each characteristic voltage; if not, the system is judged to be in single-phase grounding, and the three phase grounding phases with the minimum absolute value of phase difference are obtained. And the output voltage of the active compensator is utilized to accurately judge the grounding and fault phases according to the phase change of the neutral point voltage of the detection system.

Description

Single-phase grounding judgment and phase judgment method of neutral point ungrounded system
Technical Field
The application relates to the technical field of single-phase grounding judgment of a power grid system, in particular to a single-phase grounding judgment and phase judgment method of a neutral point ungrounded system.
Background
In a power distribution network, a single-phase earth fault is a common system fault with the highest occurrence probability. When single-phase grounding occurs, a large current flows through the grounding point, and a grounding arc may be generated. Because the grounding current is large, the electric arc can not be extinguished by self, and 3-3.5 times of overvoltage is generated, thereby bringing great risk to the equipment of the power system and the personal safety. Arc suppression coils are used in large numbers to extinguish grounded arcs. But the arc suppression coil can only counteract grounding point capacitive current. After the arc suppression coil is compensated, residual current exists in the grounding point, and a larger personal electric shock risk still exists. In recent years, single-phase grounding active compensators based on power electronics technology have been developed rapidly. The active compensation can completely compensate the current of the single-phase grounding point, thereby ensuring the personal safety and not influencing the power supply reliability, and the active compensation is an advanced single-phase grounding compensation mode of the power distribution network.
In the active compensation mode, whether the system is in single-phase grounding or not must be accurately judged, and the grounding phase must be accurately judged, so as to perform accurate compensation. The traditional method for judging whether the system is in single-phase grounding mainly comprises a zero-sequence voltage threshold value method, a zero-sequence current threshold value method and the like. The zero sequence voltage threshold method is characterized in that a voltage threshold is set, when the zero sequence voltage of a system exceeds the threshold, the system is considered to be in single-phase grounding, and otherwise, the system is considered not to be in single-phase grounding. The threshold judgment method is the most common method, and can be used for a simple and effective grounding judgment method of a neutral point ungrounded system or an arc suppression coil grounded system. The zero sequence current threshold value method is mainly applied to an arc suppression coil grounding system. When the system is in single-phase grounding, the current flowing through the arc suppression coil loop is obviously increased, and when the current exceeds a preset threshold value, the system is considered to be in single-phase grounding.
According to the traditional method for judging the single-phase grounding phase of the system, a lagging phase of the phase with the highest amplitude in three-phase voltage is considered as a grounding phase under the condition of under-compensation according to the compensation state (over-compensation or under-compensation) of the system; and under the overcompensation state, the leading phase of the phase with the highest amplitude in the three-phase voltage is grounded. However, the above conventional method has a limited application in the active compensation mode. In the active compensation mode, a compensation value is calculated, and a voltage for detection is output through an active compensator when a system normally operates. Since the internal resistance of the active compensator is low, the neutral point potential is clamped near the output voltage of the active compensator when the output voltage of the active compensator is determined. If the system is in single-phase grounding at the moment, the voltage of a neutral point of the system is not obviously changed, whether the system is grounded or not can not be judged through the voltage of the neutral point (zero sequence voltage) of the system, the grounding current can not be compensated in time, meanwhile, due to the clamping effect of the active compensator, the phase voltage phase is unchanged after the single-phase grounding, the traditional method for judging the grounding phase is not applicable any more, and the judgment can not be accurately carried out.
Disclosure of Invention
The application provides a single-phase grounding judgment and phase judgment method for a neutral point ungrounded system, which aims to solve the technical problems that the traditional judgment method is not applicable any more and cannot accurately judge.
In order to solve the technical problem, the application discloses the following technical scheme:
a single-phase grounding judgment and phase judgment method of a neutral point ungrounded system comprises the following steps: connecting an external voltage source to a system neutral point to obtain a first detection voltage, a second detection voltage and a third detection voltage output by the external power source; according to the first detection voltage, the second detection voltage and the third detection voltage, respectively obtaining a first characteristic voltage reference value of a neutral point under the action of the first detection voltage, a second characteristic voltage reference value of the neutral point under the action of the second detection voltage and a third characteristic voltage reference value of the neutral point under the action of the third detection voltage; respectively obtaining a current value of a first characteristic voltage of a neutral point under the action of the first detection voltage, a current value of a second characteristic voltage of the neutral point under the action of the second detection voltage and a current value of a third characteristic voltage of the neutral point under the action of the third detection voltage according to the first detection voltage, the second detection voltage and the third detection voltage; calculating and obtaining a first phase difference between the current value of the first characteristic voltage and the reference value of the first characteristic voltage, a second phase difference between the current value of the second characteristic voltage and the reference value of the second characteristic voltage, and a third phase difference between the current value of the third characteristic voltage and the reference value of the third characteristic voltage; judging whether the number of phase difference absolute values exceeding a preset phase difference threshold value in the three phase differences is less than or equal to 1; if so, taking the current value of the first characteristic voltage as a reference value of the first characteristic voltage, taking the current value of the second characteristic voltage as a reference value of the second characteristic voltage, and taking the current value of the third characteristic voltage as a reference value of the third characteristic voltage; if not, the system is judged to be in single-phase grounding, and the three phase grounding phases with the minimum absolute value of phase difference are obtained.
Optionally, the calculating to obtain a first phase difference between the current value of the first characteristic voltage and the reference value of the first characteristic voltage, a second phase difference between the current value of the second characteristic voltage and the reference value of the second characteristic voltage, and a third phase difference between the current value of the third characteristic voltage and the reference value of the third characteristic voltage includes:
wherein, the angle is U1now、∠U2nowAnd U3nowPhase angles of a current value of the first characteristic voltage, a current value of the second characteristic voltage and a current value of the third characteristic voltage respectively are equal to U1base、∠U2baseAnd U3baseA phase angle that is the first characteristic voltage reference value, the second characteristic voltage reference value, and the third characteristic voltage reference value,andis the phase difference between the current value and the reference value.
Optionally, the preset phase difference threshold is 0 ° to 0.1 °.
Optionally, the first detection voltage, the second detection voltage and the third detection voltage respectively correspond to three phases of a system.
Optionally, the amplitudes of the first detection voltage, the second detection voltage, and the third detection voltage are the same and are respectively 2% to 15% of the nominal phase voltage of the system.
Has the advantages that: the application provides a single-phase grounding judgment and phase judgment method of a neutral point ungrounded system. And secondly, respectively obtaining a first characteristic voltage reference value of the neutral point under the action of the first detection voltage, a second characteristic voltage reference value of the neutral point under the action of the second detection voltage and a third characteristic voltage reference value of the neutral point under the action of the third detection voltage according to the first detection voltage, the second detection voltage and the third detection voltage. And respectively obtaining a current value of a first characteristic voltage of the neutral point under the action of the first detection voltage, a current value of a second characteristic voltage of the neutral point under the action of the second detection voltage and a current value of a third characteristic voltage of the neutral point under the action of the third detection voltage according to the first detection voltage, the second detection voltage and the third detection voltage. And thirdly, calculating and obtaining a first phase difference between the current value of the first characteristic voltage and the reference value of the first characteristic voltage, a second phase difference between the current value of the second characteristic voltage and the reference value of the second characteristic voltage, and a third phase difference between the current value of the third characteristic voltage and the reference value of the third characteristic voltage. And finally, judging whether the number of phase difference absolute values exceeding a preset phase difference threshold value in the three phase differences is less than or equal to 1. If so, taking the current value of the first characteristic voltage as a reference value of the first characteristic voltage, taking the current value of the second characteristic voltage as a reference value of the second characteristic voltage, and taking the current value of the third characteristic voltage as a reference value of the third characteristic voltage; if not, the system is judged to be in single-phase grounding, and the three phase grounding phases with the minimum absolute value of phase difference are obtained. According to the method and the device, the output voltage of the active compensator is utilized, and grounding judgment and fault phase judgment are accurately carried out according to the phase change of the neutral point voltage of the detection system.
Drawings
In order to more clearly explain the technical solution of the present application, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious to those skilled in the art that other drawings can be obtained according to the drawings without any creative effort.
Fig. 1 is a flowchart of a single-phase grounding judgment and phase judgment method for a neutral point ungrounded system;
fig. 2 is an example diagram of a single-phase grounding judgment and phase judgment method for a neutral-point ungrounded system.
Detailed Description
Referring to fig. 1, a flowchart of a single-phase grounding determining and phase determining method for a neutral point ungrounded system is provided in the present application, and it can be known that the present application provides a single-phase grounding determining and phase determining method for a neutral point ungrounded system, the method includes:
s01: and connecting an external voltage source to a system neutral point to obtain a first detection voltage, a second detection voltage and a third detection voltage output by the external power source.
The first detection voltage, the second detection voltage and the third detection voltage respectively correspond to three phases of a system. The amplitudes of the first detection voltage, the second detection voltage and the third detection voltage are the same and are respectively 2% -15% of the nominal phase voltage of the system.
S02: and respectively obtaining a first characteristic voltage reference value of the neutral point under the action of the first detection voltage, a second characteristic voltage reference value of the neutral point under the action of the second detection voltage and a third characteristic voltage reference value of the neutral point under the action of the third detection voltage according to the first detection voltage, the second detection voltage and the third detection voltage.
S03: and respectively obtaining a current value of a first characteristic voltage of the neutral point under the action of the first detection voltage, a current value of a second characteristic voltage of the neutral point under the action of the second detection voltage and a current value of a third characteristic voltage of the neutral point under the action of the third detection voltage according to the first detection voltage, the second detection voltage and the third detection voltage.
S04: and calculating to obtain a first phase difference between the current value of the first characteristic voltage and the reference value of the first characteristic voltage, a second phase difference between the current value of the second characteristic voltage and the reference value of the second characteristic voltage, and a third phase difference between the current value of the third characteristic voltage and the reference value of the third characteristic voltage.
Calculating a first phase difference between the current value of the first characteristic voltage and the reference value of the first characteristic voltage, a second phase difference between the current value of the second characteristic voltage and the reference value of the second characteristic voltage, and a third phase difference between the current value of the third characteristic voltage and the reference value of the third characteristic voltage, including:
wherein, the angle is U1now、∠U2nowAnd U3nowPhase angles of a current value of the first characteristic voltage, a current value of the second characteristic voltage and a current value of the third characteristic voltage respectively are equal to U1base、∠U2baseAnd U3baseA phase angle that is the first characteristic voltage reference value, the second characteristic voltage reference value, and the third characteristic voltage reference value,andis the phase difference between the current value and the reference value.
S05: and judging whether the number of the phase difference absolute values exceeding a preset phase difference threshold value in the three phase differences is less than or equal to 1.
The preset phase difference threshold value is 0-0.1 degrees.
S06: if so, taking the current value of the first characteristic voltage as a first characteristic voltage reference value, taking the current value of the second characteristic voltage as a second characteristic voltage reference value, and taking the current value of the third characteristic voltage as a third characteristic voltage reference value.
S07: if not, the system is judged to be in single-phase grounding, and the three phase grounding phases with the minimum absolute value of phase difference are obtained.
The application provides a single-phase grounding judgment and phase judgment method of a neutral point ungrounded system. And secondly, respectively obtaining a first characteristic voltage reference value of the neutral point under the action of the first detection voltage, a second characteristic voltage reference value of the neutral point under the action of the second detection voltage and a third characteristic voltage reference value of the neutral point under the action of the third detection voltage according to the first detection voltage, the second detection voltage and the third detection voltage. And respectively obtaining a current value of a first characteristic voltage of the neutral point under the action of the first detection voltage, a current value of a second characteristic voltage of the neutral point under the action of the second detection voltage and a current value of a third characteristic voltage of the neutral point under the action of the third detection voltage according to the first detection voltage, the second detection voltage and the third detection voltage. And thirdly, calculating and obtaining a first phase difference between the current value of the first characteristic voltage and the reference value of the first characteristic voltage, a second phase difference between the current value of the second characteristic voltage and the reference value of the second characteristic voltage, and a third phase difference between the current value of the third characteristic voltage and the reference value of the third characteristic voltage. And finally, judging whether the number of phase difference absolute values exceeding a preset phase difference threshold value in the three phase differences is less than or equal to 1. If so, taking the current value of the first characteristic voltage as a reference value of the first characteristic voltage, taking the current value of the second characteristic voltage as a reference value of the second characteristic voltage, and taking the current value of the third characteristic voltage as a reference value of the third characteristic voltage; if not, the system is judged to be in single-phase grounding, and the three phase grounding phases with the minimum absolute value of phase difference are obtained. According to the method and the device, the output voltage of the active compensator is utilized, and grounding judgment and fault phase judgment are accurately carried out according to the phase change of the neutral point voltage of the detection system.
Referring to fig. 2, an example diagram of a single-phase grounding judgment and phase judgment method for a neutral point ungrounded system is provided, wherein Ua, Ub and Uc are three-phase voltage of the system, and U is a phase voltage of the systemn1,Un2,Un3Is a first characteristic voltage reference value, a second characteristic voltage reference value and a third characteristic voltage reference value, Un1_n,Un2_n,Un3_nThe current values are the current value of the first characteristic voltage, the current value of the second characteristic voltage and the current value of the third characteristic voltage.
Taking the C-phase single-phase grounding as an example, the process of judging the single-phase grounding and the phase according to the technical scheme of the patent is as follows:
referring to fig. 2- (1), when the system operates normally, the three-phase voltages are Ua ═ 5800V ═ 0 °, Ub ═ 5800kV ═ 120 °, and Uc ═ 5800kV ═ 120 °.
Referring to fig. 2- (2), the external power supply outputs a first detection voltage Ut1The angle is 200V < 0 degrees, corresponding to the phase A of the system. The reference value of the first characteristic voltage of the neutral point is 119.8V-0.8 degrees.
Referring to fig. 2- (3), the external power supply outputs a second detection voltage of Ut2200V-120 degrees, corresponding to the B phase of the system. The reference value of the second characteristic voltage of the neutral point is 119.8V-120.8 degrees.
Referring to fig. 2- (4), the external power supply outputs a third detection voltage of Ut3200V & lt 120 DEG, corresponding to the C phase of the system. The reference value of the third characteristic voltage of the neutral point is 119.8V < 119.2 degrees.
Referring to fig. 2- (5), the system is single-phase grounded with a ground resistance of 1000 Ω. The current values of the first characteristic voltage, the second characteristic voltage and the third characteristic voltage of the neutral point are respectively 119V-3.6 degrees, 118V-118 degrees and 117.6V-119.3 degrees.
The phase difference between the current value and the reference value is calculated to be-2.8 degrees, 2.8 degrees and 0.1 degrees respectively.
According to the technical scheme, two of the three absolute phase difference values exceed a preset phase difference threshold value, and the system is considered to be in single-phase grounding. And considering that the phase difference absolute value corresponding to the third characteristic voltage is minimum, and considering that the phase C is grounded in a single phase.
Other embodiments of the present application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. This application is intended to cover any variations, uses, or adaptations of the application following, in general, the principles of the application and including such departures from the present disclosure as come within known or customary practice within the art to which the application pertains. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the application being indicated by the following claims.
It will be understood that the present application is not limited to the method steps that have been described above and illustrated in the accompanying drawings, and that various modifications and changes can be made without departing from the scope thereof. The scope of the application is limited only by the appended claims.

Claims (4)

1. A single-phase grounding judgment and phase judgment method of a neutral point ungrounded system is characterized by comprising the following steps:
connecting an external voltage source to a system neutral point to obtain a first detection voltage, a second detection voltage and a third detection voltage output by the external power source, wherein the first detection voltage, the second detection voltage and the third detection voltage respectively correspond to three phases of the system;
when the system normally operates, according to the first detection voltage, the second detection voltage and the third detection voltage, respectively obtaining a neutral point first characteristic voltage reference value under the action of the first detection voltage, a neutral point second characteristic voltage reference value under the action of the second detection voltage and a neutral point third characteristic voltage reference value under the action of the third detection voltage;
when the system is in current operation, according to the first detection voltage, the second detection voltage and the third detection voltage, respectively obtaining a current value of a first characteristic voltage of a neutral point under the action of the first detection voltage, a current value of a second characteristic voltage of the neutral point under the action of the second detection voltage and a current value of a third characteristic voltage of the neutral point under the action of the third detection voltage;
calculating and obtaining a first phase difference between the current value of the first characteristic voltage and the reference value of the first characteristic voltage, a second phase difference between the current value of the second characteristic voltage and the reference value of the second characteristic voltage, and a third phase difference between the current value of the third characteristic voltage and the reference value of the third characteristic voltage;
judging whether the number of phase difference absolute values exceeding a preset phase difference threshold value in the three phase differences is less than or equal to 1;
if so, taking the current value of the first characteristic voltage as a reference value of the first characteristic voltage, taking the current value of the second characteristic voltage as a reference value of the second characteristic voltage, and taking the current value of the third characteristic voltage as a reference value of the third characteristic voltage;
if not, the system is judged to be in single-phase grounding, and the three phase grounding phases with the minimum absolute value of phase difference are obtained.
2. The method of claim 1, wherein calculating a first phase difference between the current value of the first characteristic voltage and the reference value of the first characteristic voltage, a second phase difference between the current value of the second characteristic voltage and the reference value of the second characteristic voltage, and a third phase difference between the current value of the third characteristic voltage and the reference value of the third characteristic voltage comprises:
wherein, the angle is U1now、∠U2nowAnd U3nowPhase angles of a current value of the first characteristic voltage, a current value of the second characteristic voltage and a current value of the third characteristic voltage respectively are equal to U1base、∠U2baseAnd U3baseA phase angle that is the first characteristic voltage reference value, the second characteristic voltage reference value, and the third characteristic voltage reference value,andis the phase difference between the current value and the reference value.
3. The method as claimed in claim 1, wherein the predetermined phase difference threshold is 0 ° to 0.1 °.
4. The method according to claim 1, wherein the first, second and third voltages have the same amplitude, which is 2-15% of the nominal phase voltage of the system.
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